Two-cycle engine transfer and exhaust port arrangement



F. T. IRGENS April 3, 1956 TWO-CYCLE ENGINE TRANSFER AND EXHAUST PORT ARRANGEMENT Filed July 18, 1951 2 Sheets-Sheet l I N V EN TOR. FIN/V 7? A? GEN.

April 3, 1956 T N 2,740,390

TWO-CYCLE ENGINE TRANSFER AND EXHAUST PORT ARRANGEMENT Filed July 18, 1951 2 Sheets-Sheet 2 Mi zu, Mbawm A 7702M; v5

Unitfid Stat tent TWO-CYCLE ENGINE TRANSFER AND EXHAUT PORT ARRAYGEIVIENT Finn T. Irgens, Wauwatosa, Wis., assignor to Outboard, Marine & Manufacturing Company, Waukegan, 1th., a corporation of Delaware Application July 18, 1951, Serial No. 237,343

9 Claims. (Cl. 123-73) This invention relates to a two-cycle engine transfer and exhaust port arrangement.

The invention has particular reference to two-cycle engines of relatively low power, wherein it is practicable to use loop scavenging without a piston deflector and with all of the inlet and exhaust ports concentrated at one side of the cylinder. In such an engine, the present invention contemplates that the transfer and exhaust ports will be drilled or cored into the cylinder from a common surface at different levels or angles so that the transfer ports will communicate with the transfer passage leading from the crank case, the exhaust port being offset from such pasage. it is further contemplated that the exhaust pipe flange which connects the exhaust pipe to the cylinder block will be used to hold to the cylinder block a gasket which not only performs the usual functions of a gasket but also serves to cover the unused end portions of the bores which provide the transfer .ports.

By this arrangement, the expense of making the transfer and exhaust ports is low, the length of the exhaust passage in the cylinder is reduced to a minimum, heat transfer between the exhaust pipe and the cylinder is reduced by the presence of the gasket, and there is considerable heat exchange through the metal between the exhaust and transfer ports, whereby the exhaust gases are desirably cooled and the incoming mixture is desirably pre-heated, with resultant expansion and increased scavenging effect.

In the past, where loop scavenging has been used, the transfer ports are usually in greater number than those here required and the ports are usually extended angularly about the cylinder, thus increasing the difliculty of coring them either in a die cast or sand cast cylinder block. It will be observed that through the use of the present invention all of the ports open through the surface to which the exhaust manifold gasket is later applied to cover those used for transfer.

In the drawings:

Fig. 1 is a view in side elevation of a two-cycle engine embodying the invention, portions of its starting pulley being broken away and its exhaust manifold and gasket being omitted, whereby to expose the finished surface to which the gasket is applied.

Fig. 2 is a view taken in section on the line 2-2 of Fig. 1.

Fig. 3 is a view taken in section on the line 3-3 of Fig. 1.

Fig. 4 is a view on the line 44 of Fig. 1.

Fig. 5 is a view on the line 5-5 of Fig. 1.

Fig. 6 is a detail view in elevation of the exhaust port gasket and transfer port closure.

The two-cycle engine may be of generally conventional construction. In the device disclosed, there is a mounting bracket 4 supporting the crank case 5 which has bearings for a crank shaft 6. Connected to the crank 7 by means of connecting rod 8 is a piston 9 reciprocable in the engine cylinder. The cylinder block 10 has a combustion chamber 101 and a liner 102. At one projecting end, the crank shaft 6 carries a power delivering pulley 11 and a starting rope pulley l2, neither of which concerns the present invention. At its other projecting end, the shaft carries a fly wheel and blower fan 13 and power delivering pulley 14. The shroud 15 is apertured at 16 to receive cooling air which is impelled by the fly wheel vanes 17 and guided by shroud 15 across the fins 18 and 19 of cylinder 10 for the cooling of the cylinder. Carburetor 1, connected beneath the crank case 5 as best shown in Fig. 1, has an air duct 2 leading into the crank case subject to reed-type intake valve means at 3. The invention is not concerned with any of this structure.

As best shown in Fig. 5, the crank case is enlarged at 20 to provide a cavity with which communicate the transfer passages 21 in the cylinder block, these being desirably cored therein. The form of the transfer passage means 21 (Fig. 1) is such that they clear the position in which the exhaust port 22 is bored through the cylinder block into the cylinder from the external surface 23. There are desirably two separate passages at 21 only because the intervening partition 210 aids in heat transfer and thereby facilitates exhaust port cooling.

At positions laterally offset from the exhaust port 22, I bore the transfer port holes 24 which preferably extend at an upward angle from the finished surface 23 to enter the cylinder 10 at opposite sides of the exhaust port 22 and immediately adjacent thereto, and at a slightly lower level than exhaust port 22.

When the engine is assembled, an exhaust port gasket 25 is applied to the finished face 23, such gasket being apertured at 26 in registry with exhaust port 22. The gasket is not, however, limited in extent to the area immediately surrounding the exhaust port, but desirably registers with the entire finished surface 23 and is held thereto by a correspondingly extended flange 27 with which the exhaust pipe 28 is provided. As a result, the gasket and flange together completely cover the unused ends of the bores 24 which provide the transfer ports. The latter thus serve only to provide communication from the transfer passages 21 into the cylinder 10. Inasmuch as the metal remaining about the exhaust port 22, and between such port and the passages 21, is relatively thin, heat transfer will occur very efiectively through this web between the hot gases in the exhaust port and the gases in the transfer passages 21 and transfer ports 24, the latter gases usually being considerably below atmospheric temperature due to the evaporation of the fuel.

Not only is the exhaust port 22 relatively short, but its external surfaces are quite effectively cooled by this construction, and the scavenging action of the incoming mixture is increased by such expansion as occurs as a result of the transfer to the mixture of heat from the exhaust gases.

The fact that the exhaust port is at a higher level than the transfer ports 24 permits the escape of exhaust gases to start before the newly arriving mixture is admitted. Thus, there is no back pressure at the time of scavenging.

While the method of manufacture has been described above, it may be summarized as follows:

After the cylinder block is complete, usually by sand casting or die casting it about the lining sleeve 192, and boring the passages 21, the face 23 is surfaced and the bores 22 and 24 are drilled into such face and through the liner to the combustion chamber 101. The crank case is then assembled with the crank shaft and rotary parts carried thereby, the connecting rod and piston being assembled with the crank, and the cylinder being assembled to the crank case. The gasket 25 cut to fit the finished surface at 23 and having a central aperture at 26 in registry with the exhaust bore 22, is now attached to the cylinder block by clamping it in place between the cylinder block and the flange 27 of exhaust pipe 28, the flange being anchored by the cap screws 29 3 as shown in Fig. 3. Since the apertured gasket freely passes the exhaust gases to pipe 28, but serves as a complete closure for the ends of bores 24, closed communica tion is provided from the transfer passages Zito the.

cylinder. The gases are admitted to the cylinder substantially tangentially at opposite sides of the exhaust port block between the cylinder cavity and said surface, said block having exhaust and transfer holes extending. from said surface to the cavity, an exhaust hole being spaced from and a transfer hole intersecting said passage.

2. As a new article of manufacture, a two-cycle internal combustion engine cylinder block having an axially extending cylinder cavity an axially extending transfer passage within said bloclt and a generally radially extending exhaust hole adjacent the transfer passage but offset out of communication therewith, said block further having a transfer hole generally tangential to said cylinder cavity and adjacent the exhaust hole, said block being provided with a substantially planiform side facing surface constituting a common terminus for said exhaust and transfer holes, said transfer hole extending from said common block side through the transfer passage to the cylinder cavity in immediate proximity to the exhaust hole.

3. As a new article of manufacture,'a cylinder block for a two-cycle loop-scavenged internal combustion engine, said block having a cylinder cavity and transfer passage means Within said block and generally paralleling the cavity, said transfer passage means having terminal portions spaced circumferentially about said cylinder cavity higher than a terminal portion of said passage means intermediate its circumferentially spaced terminal portions, said block further having a generally radial exhaust hole opening from the cylinder cavity through the block above the level of said intermediate terminal portion of said transfer passage means and between the circumferentially spaced higher terminal portions of said transfer passage means, the said block further having nearly tangential transfer holes opening into the cylinder cavity from the circumferentially spaced terminalportions of said transfer passage means at opposite sides of the exhaust hole.

4. The article defined in claim 3 in which the exhaust hole is at a somewhat higher level than the transfer holes.

5. The article defined in claim 3 in which the transfer holes are upwardly inclined but lie in planes substantially parallel to each other and to the axis of the cylinder cavity and to the exhaust hole.

6. The article defined in claim 3 in which the said block has a common external face from which all of the several holes open.

7. A two-cycle engine cylinder block having a cylinder cavity and a finished external face at one side of the cavity and further having transfer passage means wholly enclosed by integral portions of said block and lying between said cavity and a portion of said face, said block having a plurality of holes opening through said face into said cavity, at least one of which holes intersects said transfer passagemeans between said face and cavity and at least one other of which is offset from said transfer means, and means providing a ported exhaust pipe connection in contact with said face and having face portions covering each such holeintersecting said transfer means, at least one such offset hole being in communication with theport of'saidexhaust 'pipe connection for venting exhaust gases from-. said cylinder cavity.

8. The device of claim 7 in further combination with a gasket clamped between said connection and said finished face, and ported in registry with the port of said connection, thegasket being continuous about each hole intersecting the transfer passage means, each hole last mentioned being upwardly inclined into the cylinder cavity from said face and opening olf center into the cylinder cavity.

9. The combination with a two-cycle internal combustion engine cylinder block having a cylinder cavity of a finished face at one side, a generally radial exhaust port opening from said cavity through said face, transfer ports opening substantially tangentially from said cavity through said block to said face atopposite sides of the exhaust port, said block further having separate transfer passages within said block and extending axially of the block beside its cylinder cavity and between its cylinder cavity and said face and intersecting only the transfer ports intermediate thelength of said transfer ports and at opposite sides of the exhaust port, a gasket contacting said face and covering the ends of said transfer ports and apertured in registry with the exhaust port, and an exhaust fitting. connected to the block in clamping engagement to the gasket and registering with the gasket aperture for communication therethrough with the exhaust port.

References Cited in the file of this patent UNITED STATES PATENTS 1,360,383 Edwards Nov. 30, 1920 1,782,567 Farmer Nov. 25, 1930 1,935,109 Brown Nov. 14, 1933 2,146,919 Stihl Feb. 14, 1939 2,169,652 Ljungstrom Aug. 15, 1939 2,331,554 Irgens Oct. 12,. 1943 2,406,404 Ryde Aug. 27, 1946 2,478,818 Geiger et al. Aug. 9, 1949 2,497,788 Mueller Feb. 14, 1950 2,500,340 Boulton Mar. 14, 1950 2,516,031 Talvio July 18, 1950 FOREIGN PATENTS 27,579 Switzerland Dec. 3, 1902 

